1. Field of the Invention
The present invention relates to a digital angle detection system using a resolver as a sensor. More particular, this invention is concerned with a novel improvement for providing a digital angle output that is stable and the least affected by a cable length or the like.
2. Description of the Related Art
In general, conventional digital angle detection systems fall into a tracking type and a phase type, A typical example of a phase type system has the configuration shown in FIG. 1.
A single-phase resolver signal sin(.omega. t-.theta.), which is provided by a resolver 2 that is a rotor detector and that receives two excitation signals of different phases sin.omega. t and cos.omega. t from a two-phase exciter 1, is fed to a phase comparator 4 via a waveform shaper 3. An output signal 4a of the phase comparator 4 passes through a loop filter 5, a variable frequency generator 6, and an output counter 7. A digital angle output .phi. (where .phi. equals to .theta.) ensues. A subtracter 8 linked to the output counter 7 is connected to a ring counter 9 that is linked to the two-phase exciter 1.
Because of the foregoing configuration, the conventional digital angle detection system has problems described below.
To be more specific, a resolver that inputs two excitation signals of different phases and outputs one single-phase voltage is used to detect an angle as a phase difference of a resolver signal and transfer the angle information. The precision of the angle information is dependent greatly on an impedance on a signal transmission line, which is determined with a cable length from the resolver to a signal processor, or on a temperature change. It is very hard to provide a high-precision digital angle output. Moreover, a two-phase exciter is indispensable. This leads to complex circuitry and high cost.